Ice and supercooled water detection system

ABSTRACT

A system for detecting ice or supercooled large droplets within an area of interest having a detection system measuring radiance or reflectance of the area of interest when exposed to shortwave infrared radiation having a wavelength in the range of about 2.05 μm to about 2.30 μm. The detection system measures the radiance or reflectance in a first band having a wavelength in the range of about 2.05 μm to about 2.15 μm and outputting a first band signal, and further measures the radiance or reflectance in a second band having a wavelength in the range of about 2.15 μm to about 2.30 μm and outputting a second band signal. A processing unit determines a ratio of the first band signal and the second band signal and compares the ratio to a predetermined critical ratio and outputs a determination signal indicating presence of ice or supercooled water droplets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/895,040, filed on Oct. 24, 2013. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to an optical system capable of detectingice on a wide variety of surfaces, such as bridges, roads, sidewalks,railways, runaways, for use with ground-based vehicles and furthercapable of detecting supercooled water droplets that freeze whenimpacting the surfaces of airborne vehicles, such as aircrafts, UnmannedAir Vehicles (UAVs) and other objects of interest.

BACKGROUND AND SUMMARY

This section provides background information related to the presentdisclosure that is not necessarily prior art. This section furtherprovides a general summary of the disclosure, and is not a comprehensivedisclosure of its full scope or all of its features.

The detection of ice and associated icing conditions is an importantfactor in maximizing safety associated with various modes oftransportation. It is well known that ice accumulation on surfaces canlead to an increased occurrence of vehicle accidents, personal injuriesresulting from falls, and disruptions in transportation and other humanactivities.

In connection with vehicle travel, roadway ice can often occur in inways that are difficult for a prudent driver to detect. Such ice—oftenreferred to as ‘slippery ice’ or ‘black ice’—is usually smooth andtranslucent. Similarly, in connection with aircraft travel, airborneicing conditions can often occur in ways that are difficult for a pilotto discern. Airborne icing can occur in nearly all regions of the globethroughout the year, making detection and avoidance important for flightsafety.

Unfortunately, few systems exist that are capable of reliably detectingthe presence of ice or icing conditions and providing an associatedalert. In terms of ground-based vehicles, such as cars, trucks, trains,automated people movers, rails, monorails, metros, buses, motorcycles,bicycles, and similar vehicles, there is a surprising lack of suitablesystems for detecting and warning users of the presence of ice onsurfaces, such as roadways, bridges, railways, sidewalks, or eventaxiways (such as in connection with ground operations of aircraft). Infact, ice detection in most vehicles merely includes a simplenotification once the air temperature is at or near the freezing pointof water. However, unfortunately, this is not typically indicative ofthe presence of surface ice that may affect safety and/or drivability ofa vehicle. This invariably leads to a high number of accidents andfatalities due to drivers and operators being unaware of deterioratingconditions or false alerts that are ultimately disregarded by a driveror operator. In terms of airborne-based vehicles, such as aircrafts,helicopters, UAVs, and similar vehicles, additional systems areavailable, but each suffers from a number of disadvantages.

Prior art approaches for detecting slippery ice on surfaces, such asroads, use an imager capable of measuring the polarization of the lightreflected by slippery ice. However, it should be understood thatalthough light is polarized when reflected by dielectric materials, suchas ice, ice is not the only dielectric material that polarizes light. Infact, reflections by wet and/or oily surfaces also cause polarization,which would lead to false reporting of ice. Therefore, polarization isnot capable of distinguishing among the possible types of dielectricmaterials reflecting light. Consequently, it cannot be used to detectthe presence of ice unambiguously. For example, U.S. Pat. No.2008/0129541A1 refers to a slippery ice warning system capable ofmonitoring the road ahead of a vehicle. One or two cameras are used toimage the same scene at two orthogonal polarizations. When a singlecamera is used, a polarization beam splitter is used to separate thereflected light into two orthogonal polarizations. The possible (butambiguous) determination of the existence of slippery ice ahead of thevehicle is detected by measuring the polarization of the reflectedlight. However, again, this system is unable to discern whether thedetected polarization is due to ice or some other reflective material.

Additional ice detection systems are based on in-situ measurements andare only applied to airborne applications. For example, U.S. Pat. No.7,104,502 is for a system capable of detecting the accumulation of iceby measuring changes in the vibration frequency of a strut exposed tothe airflow on an aircraft. The strut contains at least one feature thatallows ice to accrete on it at higher rate than in other parts of theaircraft. Similarly, U.S. Pat. No. 7,370,525 refers to a dual channelinflight system that detects ice accretion on aircraft surfaces. Thesystem illuminates the surface of the aircraft with linearly polarizedlight. Light conductors with polarization sensitivity aligned to thetransmitted light, and with polarization sensitivity orthogonal to it,acquire the backscattered light. The ratio of the intensities of thelight in the two conductors is used to detect the presence of ice.

Moreover, U.S. Pat. No. 6,269,320 describes an in-situ Supercooled LargeDroplet (SLD) detector. This system takes advantage of boundary layerflow patterns to detect SLD. It is capable of distinguishing between thepresence of water droplets that cause regular cloud icing and SLD icing.However, this system detects ice after it accumulates on aircraftssurfaces and thus does not give warnings before a hazards situationoccurs. In particular, it does not detect supercooled liquid waterdroplets in the airspace around aircrafts.

In some cases, prior art approaches for distinguishing between liquidwater and ice particles in the airspace ahead of aircrafts measure thedepolarization of the backscattered light emitted by a polarized laserbeam. U.S. Pat. No. 6,819,265 refers to an ice warning system capable ofmonitoring the airspace ahead of the aircraft. The system contains alaser source, optical elements to direct the laser beam into theairspace ahead of the aircraft and to receive the laser lightbackscattered by the targets, optical elements to separate the receivedlaser light into various wavelengths and to direct them into lightdetectors, and a processor to conduct the calculations necessary togenerate warnings. U.S. Pat. No. 7,986,408 refers to an airborne activesystem that employs both linear and circular polarizations to detectwater droplets and ice particles in the airspace ahead of an aircraft.

According to the principles of the present teachings, an ice andsupercooled water detection system is provided that overcomes thedisadvantages of the prior art and is particularly useful inground-based and airborne-based applications. In most embodiments of thepresent teachings, the system detects ice unambiguously by makingmulti-spectral measurements of radiance. In some embodiments, the systemcan be passive but a light source can be included, detectors and/or ashortwave infrared (SWIR) camera with two filters, a data processorunit, and interfaces with displays, safety systems, and/or flightsystems provide an indication of icing and a response to it.

Still further, in some conventional airborne applications, the detectionof icing conditions in the airspace ahead of an aircraft requiressystems capable of actually distinguishing between supercooled liquidwater droplets and ice particles. Accordingly, in some embodiments ofthe present teachings, the system is capable of detecting liquid waterdroplets and ice particles in an area of interest of the airspace, andof estimating the size of potentially hazardous supercooled liquid waterdroplets. This embodiment increases aviation safety by adding thecapability of detecting icing conditions and Supercooled Large Droplets(SLD) to flight displays such as Enhanced Vision Systems (EVS).

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations. They are notintended to limit the scope of the present disclosure.

FIG. 1 is a graph showing the imaginary part of the complex index ofrefraction of liquid water and ice, indicating that reflectance (orsimple radiance as justified below) measurements at shortwave infrared(SWIR) spectral bands between about 2.00 and 2.15 μm and between about2.15 and 2.30 μm can be used to distinguish liquid water droplets fromice particles.

FIG. 2A is a probability distribution sketch illustrating that theradiance ratio (γ) can be used to distinguish water droplets from iceparticles.

FIG. 2B shows radiance ratios derived from measurements of a convectivecloud indicating that regions of liquid water can be distinguished fromregions of ice particles, based on calculations of γ, the ratio of thespectral reflectances at 2.10 μm and 2.30 μm.

FIG. 3A is a ‘Twomey diagram’ indicating that relative reflectance atabout 2.2 μm (R) can be used to estimate cloud droplet radius.

FIG. 3B is a ‘Nakajima-King diagram’ indicating that reflectance values(or radiance values) in absorbing and non-absorbing spectral bands canbe used to determine cloud droplets' size.

FIG. 4 is a flow chart of an algorithm for determining the presence ofsupercooled liquid water droplets.

FIG. 5A is a flow chart of an algorithm for determining the presence ofSupercooled Large Droplets (SLD) around and/or ahead of vehicles.

FIG. 5B is a flow chart of an algorithm for determining the presence ofSLD when larger accuracy is desirable.

FIG. 6 is a description of an algorithm for determining the presence ofice on runaways, roads and other surfaces of interest.

FIG. 7A is a block diagram of the ice and supercooled water detectionsystem according to some embodiments of the present teachings.

FIG. 7B is a block diagram of the ice and supercooled water detectionsystem according to some embodiments of the present teachings.

FIG. 8A illustrates ice and supercooled water detection system for usein connection with airborne-based applications.

FIG. 8B illustrates ice and supercooled water detection system for usein connection with ground-based applications.

FIG. 8C illustrates a simplified ice and supercooled water detectionsystem.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings. Example embodiments are provided so that thisdisclosure will be thorough, and will fully convey the scope to thosewho are skilled in the art. Numerous specific details are set forth suchas examples of specific components, devices, and methods, to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to those skilled in the art that specific details need notbe employed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

According to the principles of the present teachings, an ice andsupercooled water detection system 10 is provided having a light source12, at least one detector 14, a data processing unit 16, and an outputsystem 18. These components will be described in greater detail herein.However, it should be understood that the present teachings provideutility in a wide variety of applications, including ground-based andairborne-based applications. More particularly, and without limitation,the present teachings are well-suited for use in ground-basedapplications, including detecting ice on bridges, roadways, railways,ramps, sidewalks, building entrances, building decks, garages andparking areas, runways and taxiways, marinas, boat decks, platforms, andany other surface subject to icing. It should be understood that suchground-based applications can further monitoring at fixed locations orregions, such as on bridges, buildings, garages, roadways, or similarlocations. Moreover, the present teachings can be incorporated into anumber of ground-based vehicles, such as, but not limited to, cars,trucks, trains, automated people movers, rails, monorails, metros,buses, motorcycles, bicycles, aircraft (taxiing), and similar vehicles,and ground-based infrastructure locations, such as on poles, buildings,elevated locations, road barriers, and the like.

It should further be understood that the present teachings can beincorporated into a number of airborne-based vehicles, such as, but notlimited to, aircraft including engines, turbines, propellers, blades,air intakes, control surfaces, wings, stabilizers, and other componentsof aircraft; helicopters; UAVs; blimps; balloons (e.g. weatherballoons); and other objects of interest.

In all applications, the particular mounting location is not necessarilycrucial, so long as proper illumination and detection performance ismaintained. Therefore, the present teachings should not be regarded asbeing limited to any one particular mounting location on ground-basedvehicles, ground-based infrastructure, or airborne-based vehicles.

Fundamental Principles

At the outset, it is important to understand various fundamentalprinciples that are employed as part of the present teachings. To thisend, it should be understood that liquid water and ice exhibitfundamental characteristics when exposed to light, in particular atshortwave infrared (SWIR) spectral bands. For purposes of the presentdiscussion, these SWIR spectral bands are typically in the range ofabout 2.05 to 2.30 μm (spectrum range of interest). Generally, 2.05 μmhas been determined to be a lower limit due to the fact that theatmosphere tends to absorb a greater portion of the light below 2.05 μm,thereby negatively affecting detection efficiency. However, atwavelengths between about 2.05 and 2.30 μm atmospheric absorption isnegligible and the absorption properties of liquid water and ice exhibitpredictable characteristics (Kuo et al., 1993; Martins at al., 2007)that allows the detection of ice and liquid water as illustrated inFIG. 1. As discussed below, shortwave infrared (SWIR) spectral bandsbetween about 2.05 and about 2.15 μm and between about 2.15 and about2.30 μm can be used to distinguish liquid water droplets from iceparticles unambiguously. This range (2.05-2.30 μm) is generally referredto as a ‘water vapor window.’

Upon careful review of FIG. 1, one will note that a transition orcrossover occurs at about 2.15 μm where the absorption characteristicsof liquid water invert relative to the absorption characteristics ofice. In this way, comparison of the absorption of liquid water and icein this water vapor window or spectrum range of interest (about 2.05 μmto about 2.30 μm), specifically using measurements of reflectance orradiance obtained from opposing sides of this transition or crossoverpoint (about 2.15 μm), permits one to detect/determine the presence ofliquid water or ice unambiguously. Thus, by measuring theradiance/reflectance at wavelengths on opposing sides of this crossoverpoint, one can determine the presence of liquid water or ice based on aratio of the measured radiance/reflectance. Ideally, these regions onthe opposing sides of the crossover point provide optimal spectral bandsleading to unambiguous detection—namely a first optimal spectral band ofabout 2.05 to 2.15 μm (hereafter referred to as the 2.10 μm band) andanother optimal spectral band of about 2.20 and 2.30 μm (hereafterreferred to as the 2.25 μm band).

It should be understood that although the present teachings are directedto the measurement of radiance, measurements of reflectance cansimilarly be used. However, it should be noted that radiancemeasurements (instead of reflectance measurements) are simpler andtypically sufficient for practical applications because typical targetsof interest are illuminated with light sources containing relativelysmall or known power variations between 2.05 and 2.30 μm (e.g., cloudsor surfaces illuminated by direct or indirect sunlight, or illuminatedby a known light source). Therefore, the present teachings should not beregarded as being limited to only radiance measurements as reflectancemeasurements are also anticipated.

With reference to FIG. 2A, a probability distribution sketch is providedillustrating that a radiance ratio (γ) can be used to distinguish waterdroplets from ice particles. In some embodiments, a radiance ratio ofabout 0.40 can indicate the presence of ice particles and a radianceratio of about 0.85 can indicate the presence of water droplets. As willbe discussed herein, the exact ratio may be irrelevant so long as theradiance ratio is greater than or less than a predetermined criticalratio. Ice has a relatively low radiance ratio that allows it to bedetected when deposited on materials such as soils, concrete, andasphalt for example. With reference to FIG. 2B, radiance ratios areillustrated in connection with measurements of a convective cloudindicating regions of liquid water and ice particles, based oncalculations of γ, the ratio of the spectral reflectances at 2.10 μm and2.30 μm.

Turning now to FIG. 3A, a ‘Twomey diagram’ is provided indicating thatreflectance values (or radiance values) can be used to determine clouddroplets size. This can be achieved because, at fixed cloud opticalthickness (τ), the reflectance at around 2.2 μm (R) decreases with clouddroplet size at the rate of approximately (k r_(e))^(1/2), where k isthe absorption coefficient (the imaginary part of the index ofrefraction) of water and r_(e) is the cloud droplet (effective) radius(Twomey and Seton, 1980). The dependence of cloud reflectance on dropletsize is caused by the fact that absorption by liquid water increasesrelative to scattering with increases in droplet size. For thick clouds,the effect of changes in cloud optical thickness is negligible.Therefore, the relationship between reflectance and cloud droplet radiusprovided by the ‘Twomey diagram’ is an excellent approximation for thickclouds (clouds of large optical thickness). Measurements at otherabsorbing wavelengths can also be used to determine cloud droplet(effective) radius, for example at around 3.7 μm. The determination ofcloud droplet size can be refined using measurements of radiance at anon-absorbing wavelength as described herein.

FIG. 3B illustrates a ‘Nakajima-King diagram’ indicating thatreflectance values (or radiance values) in absorbing and non-absorbingspectral bands can be used to determine cloud droplets' size (Martins etal., 2007), even when the optical thicknesses are variable or small suchas in light drizzle or rain. The measurements at non-absorbingwavelengths also mitigate the effects of variations in illumination suchas shadowing. Rain usually occurs when r_(e)>10-15 μm, but SupercooledLarge Droplets (SLD) can have radius of up to 2.5 mm. Aircraftscertified for flights into icing conditions can handle droplets ofradius of up to about 25 μm. Unfortunately, droplets this large are notuncommon in convective clouds.

During operation, water droplets and ice particles can be detected in/onaircraft surfaces and/or airspace (immediately adjacent an aircraft whenin clouds and ahead of an aircraft when the aircraft is flying outsideclouds). To this end, as will be discussed herein, the ice andsupercooled water detection system 10 can comprise a forward lookingcamera or detector 14 for making measurements of the radiance in theaforementioned two spectral bands. In some embodiments, an in-situsensor for making measurements of the outside temperature can further beused. Algorithms are provided for detecting supercooled liquid waterdroplets and estimating the size of the droplets as described in FIGS.4, 5A and 5B.

During night operations, such as airborne-based applications, clouds inthe airspace immediately ahead of an aircraft can be illuminated withlight sources containing the desired spectrum. In some embodiments,light source 12 can be used to illuminate the airspace around theaircraft while the radiance can be measured via detector 14. In morecomplex embodiments, clouds in the airspace miles ahead of the aircraftcan be illuminated with laser beams containing the desired spectrum.However, such complexity may not be required in most applications assimpler embodiments of the present teachings can be used to detect icinghazards before ice accumulation occurs and therefore the aircraft can bemaneuvered safely away from areas of icing.

System Description

In some embodiments, as referenced herein, light source 12 can compriseany source that is capable of outputting light (or radiation energy)within a predetermined light spectrum band. As described herein, it isdesired to perform detection at a light spectrum band, or a combinationof light spectrum bands in the shortwave infrared (SWIR) spectral bands,including the range of about 2.05 μm to about 2.30 μm. Moreparticularly, in some embodiments, light source 12 can output light at asingle spectral band covering the range of interest from about 2.05 μmto about 2.30 μm. However, in some embodiments, light source 12 canoutput light covering two or more spectral bands, such as about 2.05 μmto about 2.15 μm and a second spectral band of about 2.15 μm to about2.30 μm (or about 2.20 μm to about 2.30 μm).

Still further, in some embodiments, light source 12 can comprise anylight source capable of outputting light in the shortwave infrared(SWIR) spectral bands, including lasers, halogen lights, infraredlights, light-emitting diodes, and the like. It should also beunderstood that alternative light sources can be used, such as naturallyoccurring light sources (e.g. sunlight, etc.). Therefore, it should berecognized that in some embodiments the present teachings do not requirea supplied or otherwise powered light source, but may rely on sunlightor other naturally occurring or separately provided light sources.

In some embodiments, detector 14 can comprise any suitable detector orcamera/imaging system capable of detecting and/or monitoring radianceand/or reflectance at spectral bands that allows the detection of liquidwater and/or ice. It should be understood that in some embodiments,detector 14 can be based on Indium Gallium Arsenide (InGaAs) technology,or can include or employ photodetectors, photodiodes, pyroelectricdetectors, thermopile detectors, photoconductors, and other sensors,detectors, or cameras. In some embodiments, detector 14 can comprise asingle detector, camera, or other device for measuring radiance and/orreflectance. However, in some embodiments, detector 14 can comprise twoor more detectors, cameras, or other devices that are each suitable formeasuring radiance and/or reflectance for a specific spectrum range thatis narrower than the total spectrum range of interest. In other words, afirst detector can be used to detect radiance and/or reflectance inconnection with spectrum in the about 2.05 μm to about 2.15 μm rangewhile a second detector can be used to detect radiance and/orreflectance in connection with spectrum in the about 2.20 μm to about2.30 μm range. This arrangement can permit monitoring and/or detectionto occur simultaneously when used with a light source 12 that outputsthe spectral range of interest. In some embodiments, detector 14 cancomprise one or more cameras or detectors having a filter system 20 thatemploys a plurality of filters to limit the detection of receivedwavelengths to a predetermined spectral band. That is, a filter can beused to allow light in association with the about 2.05 μm to about 2.15μm range to be detected while a second filter can be used to allow lightin association with the about 2.20 μm to about 2.30 μm range to bedetected. Irrespective of the method of measuring and/or monitoring thereflected/received light, detector 14 outputs a detector signalrepresentative to the measured radiance/reflectance.

In some embodiments, data processing unit 16 can comprise any suitableprocessing unit capable of determining a ratio of radiance measured atthe first spectral band and at the second spectral band in response tothe detector signal. Data processing unit 16 can comprise a centralprocessing unit (CPU), in some embodiments, or may further simply beimplemented through hardware design. Data processing unit 16 can furtherimplement the algorithms described herein and output an output signal.

Finally, the output signal can be received by output device 19 and, insome embodiments, further processed in connection with other vehiclesystems, such as alert displays, traction control, ABS, deicing oranti-icing equipment, or other systems or warnings.

With particular reference to FIGS. 8A, 8B, ice and supercooled waterdetection system 10 is illustrated in accordance with some embodimentsof the present teachings. Ice and supercooled water detection system 10is illustrated for particular use in connection with the detection ofsupercooled liquid water and SLD by aircrafts, helicopters and UAVs. Iceand supercooled water detection system 10 can be implemented easily inflight systems such as EVS containing cameras covering the about2.05-2.30 μm spectral band. In such embodiments, only filters in the2.10 μm and 2.25 μm spectral bands and image processing software arenecessary for the implementation of the system. These two filters can beimplemented in a chessboard like grid or in stripes. This enables thereflectance at the two spectral bands of interest to be measured innearby pixels, avoiding the need for moving parts or multiple cameras.Indeed, it allows the implementation of the ice/water detectionalgorithm while maintaining current EVS functions with only minordegradation in image resolution. In some embodiments, vertical filterstrips can be used to achieve the necessary multi-spectral measurementsalong the flight path without affecting the rest of the image.Therefore, supercooled liquid water and SLDs can be detected easily byimplementing the algorithms described in FIGS. 4, 5A and/or 5B to someexisting EVS systems.

It should be understood that the detector 14 can be mounted anywhere onthe vehicle, including the nose cone of an aircraft. Detector 14 can bemounted external or internal to the vehicle. However, it should berecognized that any protective coverings or windows 30 placed in frontof detector 14 must permit transmission of the radiance spectrum ofinterest (e.g. must be transparent to shortwave infrared). Temperaturesensors, thermostats, and/or heaters can be used with the coverings orwindows to ensure proper transmission.

With particular reference to FIG. 8B, ice and supercooled waterdetection system 10 is illustrated for particular use in connection withground-based vehicles. In some embodiments, light source 12 can bemounted under a front end of the vehicle and the corresponding detector14 can be mounted in a complementary position to detectradiance/reflectance of the light source off the surface of interest. Inthis way, the front of the vehicle can be used to maximize the angle(measured from zenith) of incidence (and reflection) on the surface.This is done to maximize reflectance because it increases with the angleof incidence.

In some embodiments, light source 12 can be mounted along a wheel welledge or other side panel and detector 14 can be mounted in a side panelor side view mirror, while maximizing reflectance. Still further, insome embodiments, ice and supercooled water detection system 10 can beused to detect ice ahead of the vehicle (rather than beneath or the sideof the vehicle). In this way, light source and detector 14 can bemounted at an elevated position and projected forward of the vehicle.

Specular reflection can be determined by imaging the area of interestahead of the vehicle with an auxiliary camera. If the radiance of anarea of the image is significantly higher (for example, a few standarddeviations above) than the mean value, these “bright” image pixels areflagged as containing specular reflection, an indication of slipperyice. Other statistical criteria could also be used to determine specularreflection. If the criteria for specular reflection are met and ice isdetected anywhere around the vehicle (γ>γ_(crit)) the image pixelscontaining specular reflection are flagged as containing slippery ice.This allows the areas ahead of the vehicle likely containing slipperyice to be mapped, displayed, and this information to be used by safetysystems and/or the driver.

With particular reference to FIG. 8C, ice and supercooled waterdetection system 10 can comprise both light source 12 and detector 14being mounted in the side mirror of a vehicle. The system is thusoptimized for simplicity in the detection of both specular reflectionand reflectance. As described herein, air or ground temperaturemeasurements can be used to further mitigate false alarms.

Methods of Ground-Based Applications

In some embodiments, a method and/or algorithm is provided for detectingslippery ice in connection with ground-based applications. Asillustrated in FIG. 6, the method can comprise the steps of:

1. A SWIR camera or detectors 14 with spectral filters between about2.05 and 2.15 μm are used to measure the radiance of the area ofinterest at about 2.10 μm (R_(2.10 μm)).

2. A SWIR camera or detectors 14 with spectral filters between about 2.2and 2.3 μm are used to measure the radiance of the area of interest atabout 2.25 μm (R_(2.25 μm)).

3. If desirable, the area of interest ahead of a vehicle or aninfrastructure is imaged in a visible or another spectral band (e.g., inthe visible band).

4. The measurements at 2.10 μm (R_(2.10 μm)) and 2.25 μm (R_(2.25 μm))are then used to produce single values or an image of the radiance ratioγ (in larger pixels than the original images if gridded filters areused). Areas on which the radiance ratio γ is smaller than apre-established critical value γ_(crit)≈0.6 (a more precise and/ordynamically adjusted value should be determined after calibration of thesystem) are flagged as containing ice. Since values can be used todetermine that ice is likely present (thereby moving to the next stepsbelow), absence of ice detection or where radiance ratio γ is largerthan the pre-established critical value γ_(crit) suggests that nowarning should be given.

5. In some embodiments, measurements of reflectance can be used todetermine the occurrence of specular reflection. For example, this canbe achieved by determining if the reflectance of a single area in thefield of view of a detector or of single image pixels is large enough(R≧R_(crit)) to be indicative of specular reflection.

6. In some embodiments, the ground temperature (T_(g)) can be measuredby an infrared sensor or estimated based on temperature measurements bya sensor exposed to the airflow. If ice and specular reflection aredetected, and T_(g)≦T_(crit)≈0° C., a visual and/or audible warningindicating the presence of ice conditions can be produced.

Methods of Airborne-Based Applications

According to some embodiments, as illustrated in FIGS. 4, 7B, and 8A,the present teachings provide a system and method for detectingsupercooled water droplets that freeze when impacting the surfaces ofaircrafts (e.g., airplanes, helicopters, blimps, UAVs) and other objectsof interest. The present teachings provide a system for detecting icinghazards in the airspace ahead of aircrafts by detecting the presence ofsupercooled liquid water droplets in this airspace, and by estimatingthe size of these droplets. As discussed herein, the present teachingsuse measurements of radiance in the two spectral bands indicated inFIGS. 1, 2A, 2B, 3A and 3B to estimate the presence of supercooledliquid water droplets in the airspace ahead of aircraft. The presentteachings provides a system that alerts a human pilot or an autopilot toicing hazards when liquid water droplets are detected in the airspaceimmediately ahead of the aircraft and the temperature is below thefreezing value.

It should be understood that the methods outlined herein are not limitedto the exact order in which they are described because, in many cases,the specific order of operation may be flexible.

In some embodiments, the present system can quantify the hazards levelby estimating the size of the supercooled liquid water droplets. Thedroplet size is estimated based on the radiance in a spectral bandaround 2.2 μm (or another absorbing spectral band such as around 3.7 μm)and analytical relationships or look up tables such as those constructedbased on the relationships depicted in FIGS. 3A and 3B. Measurements ofthe radiance in a non-absorbing spectral band, for example, around 0.67μm, can provide a more accurate estimate of the cloud droplet size.

An algorithm for detecting supercooled liquid water is described in FIG.4. It comprises of the following steps:

1. A SWIR camera or detectors with spectral filters between about 2.05and 2.15 μm are used to measure the radiance of the area ahead of theaircraft at about 2.10 μm (R_(2.10 μm)).

2. A SWIR camera or detectors with spectral filters between about 2.2and 2.3 μm at are used to measure the radiance of the area ahead of theaircraft at about 2.25 μm (R_(2.25 μm)).

3. These two measurements are then used to produce single values or animage of the radiance ratio γ (in larger pixels than the original imagesif gridded filters are used). Areas on which the radiance ratio γ islarger or equal than a pre-established critical value γ_(crit)≈0.6 (amore precise and/or dynamically adjusted value is determined aftercalibration of the system) are flagged as containing liquid waterdroplets.

4. The air temperature (T) at the flight level is measured by a sensorsuch as a thermocouple exposed to the airflow or any other suitablemethod. If the temperature is smaller or equal to a pre-establishedcritical value T_(crit)≈0° C. the areas flagged as containing liquidwater droplets are identified as contained supercooled liquid waterdroplets. Images of these areas can be colored as desired when displayed(e.g., on the MFD).

5. When the aircraft approaches areas flagged as containing supercooledliquid droplets, the system gives a warning and activates safety systemsif desirable.

The present teachings also provide a system for estimating the size ofwater droplets. The estimation of droplet size is based on radiancemeasurements and look up tables or analytical relationships constructedbased on the relationships depicted in FIGS. 3A and 3B. Algorithms forestimating the cloud droplet size (effective radius) are described inFIGS. 5A and 5B. However, it should be noted that the algorithm of FIG.5A can be improved by including measurements of radiance atnon-absorbing wavelengths (e.g., visible), whereby this measurement canthen be used as a reference to correct the radiance values used in thecalculation of the droplets' effective radius as set forth in FIG. 5B.The algorithm of FIG. 5A comprises of the steps of:

1. A SWIR camera or detectors with spectral filters between about 2.05and 2.15 μm are used to measure the radiance of the area ahead of theaircraft at about 2.10 μm (R_(2.10 μm)).

2. A SWIR camera or detectors with spectral filters between about 2.2and 2.3 μm at are used to measure the radiance of the area ahead of theaircraft at about 2.25 μm (R_(2.25 μm)).

3. These two measurements are used to produce single values or an imageof the radiance ratio γ (in larger pixels than the original images ifgridded filters are used). Areas on which the radiance ratio γ is largeror equal than a pre-established critical value γ_(crit)≈0.6 (a moreprecise and/or dynamically adjusted value should be determined aftercalibration of the system) are flagged as containing liquid waterdroplets.

4. The droplets effective radius (r_(e)) is then calculated based on themeasurements of radiance at 2.25 μm (R_(2.25 μm)) and Twomey'srelationship presented in FIG. 3A.

5. The air temperature (T) at the flight level is measured by athermocouple exposed to the airflow or any other suitable method. Areason which T_(a)≦T_(crit)≈0° C. and r_(e)≧r_(crit)≈25 μm (or a moreprecise r_(e) value determined after calibration of the system) areflagged as likely containing SLD and colored as desired when displayed(e.g., on a Multi Function Display, MFD). Areas with values ofT_(a)≦T_(crit)≈0° C. and r_(e)>>r_(crit)≈25 μm indicates extremelyhazard conditions and can be flagged as such.

A more sophisticated algorithm for detecting Supercooled Large waterDroplets (SLD) is described in FIG. 5B. The algorithm comprises thesteps of:

1. A SWIR camera or detectors with spectral filters between about 2.05and 2.15 μm are used to measure the radiance of the area ahead of theaircraft at about 2.10 μm (R_(2.10 μm)).

2. A SWIR camera or detectors with spectral filters between about 2.2and 2.3 μm at are used to measure the radiance of the area ahead of theaircraft at about 2.25 μm (R_(2.25 μm)).

3. A visible (or covering another non-absorbing spectral band) camera ordetectors with spectral filters around 0.67 μm (or another non-absorbingband) are used to measure the radiance of the area ahead of the aircraftat about 0.67 μm (R_(0.67 μm)).

4. The measurements at 2.10 μm (R_(2.10 μm)) and 2.25 μm (R_(2.25 μm))are used to produce single values or an image of the radiance ratio γ(in larger pixels than the original images if gridded filters are used).Areas on which the radiance ratio γ is larger or equal than apre-established critical value γ_(crit)≈0.6 (a more precise and/ordynamically adjusted value is determined after calibration of thesystem) are flagged as containing liquid water droplets.

5. The droplets effective radius (r_(e)) is then calculated based on themeasurements of radiance at 0.67 μm (R_(0.67 μm)) and 2.25 μm(R_(2.25 μm)), and Nakajima-King's relationship presented in FIG. 3B.

6. The air temperature (T) at the flight level is measured by athermocouple exposed to the airflow or any other suitable method. Areason which T_(a)≦T_(crit)≈0° C. and r_(e)≧r_(crit)≈25 μm (or a moreprecise r_(e) value determined after calibration of the system) areflagged as likely containing SLD and colored as desired when displayed(e.g., on a MFD). Areas with values of T_(a)≦T_(crit)≈0° C. andr_(e)>>r_(crit)≈25 μm indicates extremely hazard conditions and can beflagged as such. A visual and/or audible WARNING is produced.

In some embodiments, a WARNING can be produced when supercooled liquidwater droplets or mixtures of water droplets and ice particles aredetected, while an ALERT can be produced when SLD are detected.

It should be understood that although certain features are described inconnection with a particular application (e.g. airborne-basedapplications), this should not be regarded as limiting such certainfeatures to only the particular application, as such certain featuresmay be equally applicable to alternative applications (e.g. ground-basedapplications on vehicles or infrastructure).

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

1. A system for detecting ice and/or water within an area of interest,said system comprising: a detection system measuring radiance orreflectance of the area of interest when exposed to shortwave infrared(SWIR) radiation having a wavelength in the range of about 2.05 μm toabout 2.30 μm, said detection system measuring said radiance orreflectance in a first band having a wavelength in the range of about2.05 μm to about 2.15 μm and outputting a first band signal, saiddetection system measuring radiance or reflectance in a second bandhaving a wavelength in the range of about 2.15 μm to about 2.30 μm andoutputting a second band signal; and a processing unit determining aratio of said first band signal and said second band signal, saidprocessing unit comparing said ratio to predetermined critical ratioranges and outputting a determination signal indicating at least one ofpresence of ice when said ratio is within a first range of saidpredetermined critical ratio ranges and presence of water when saidratio is within a second range of said predetermined critical ratioranges.
 2. The system according to claim 1, further comprising: atemperature sensing system determining a temperature of the area ofinterest and outputting a temperature signal, wherein said processingunit comparing said temperature signal to a predetermined criticaltemperature range and outputting said determination signal in responsethereto.
 3. The system according to claim 1 wherein said processing unitdetermines existence of specular reflection in the area of interest,said processing unit outputting said determination signal in response tosaid specular reflection.
 4. The system according to claim 1, furthercomprising: an auxiliary camera imaging the area of interest andoutputting an auxiliary camera output, wherein said processing unitdetermines existence of specular reflection in the area of interestbased on said auxiliary camera output, said processing unit outputtingsaid determination signal in response to said specular reflection. 5.The system according to claim 1 wherein said processing unit calculatesan effective radius of water droplets detected within the area ofinterest and outputs said determination signal in response thereto. 6.The system according to claim 1, further comprising: a second detectionsystem measuring radiance or reflectance in a non-absorbing spectralband in a range of about 0.5 μm to about 0.7 μm and outputting a seconddetection system signal, wherein said processing unit uses said seconddetection system signal, said first band signal, and said second bandsignal to calculate an effective radius of water droplets detectedwithin the area of interest and outputs said determination signal inresponse thereto.
 7. The system according to claim 1, furthercomprising: a second detection system measuring radiance or reflectancein an absorbing spectral band in a range of about 3.0 μm to about 5.0 μmand outputting a second detection system signal, wherein said processingunit uses said second detection system signal, said first band signal,and said second band signal to calculate an effective radius of waterdroplets detected within the area of interest and outputs saiddetermination signal in response thereto.
 8. The system according toclaim 1 wherein said detection system comprises one or more detectors,each of said one or more detectors being sensitive to said shortwaveinfrared (SWIR) radiation having said wavelength in the range of about2.05 μm to about 2.30 μm.
 9. The system according to claim 8 whereinsaid one or more detectors comprises at least two detectors, a first ofsaid at least two detectors being sensitive to a first spectrum range ofsaid about 2.05 μm to about 2.30 μm range and a second of said at leasttwo detectors being sensitive to a second spectrum range of said about2.05 μm to about 2.30 μm range, said first spectrum range and saidsecond spectrum range being at least partially different.
 10. The systemaccording to claim 1 wherein said detection system comprises at leastone camera, said at least one camera being sensitive to said shortwaveinfrared (SWIR) radiation having said wavelength in the range of about2.05 μm to about 2.30 μm.
 11. The system according to claim 10 whereinsaid detection system further comprises two or more spectral filtersoperably coupled to said at least one camera, a first of said two ormore spectral filters being sensitive to a first spectrum range of saidabout 2.05 μm to about 2.30 μm range and a second of said at least twodetectors being sensitive to a second spectrum range of said about 2.05μm to about 2.30 μm range, said first spectrum range and said secondspectrum range being at least partially different.
 12. The systemaccording to claim 1, further comprising: a data display systemdisplaying an indicia in response to said determination signal.
 13. Thesystem according to claim 1, further comprising: a deice or anti-icingsystem of an airborne-based vehicle being responsive to saiddetermination signal.
 14. The system according to claim 1, furthercomprising: a flight control system of an airborne-based vehicle beingresponsive to said determination signal.
 15. The system according toclaim 1, further comprising: a brake control system of a ground-basedvehicle being responsive to said determination signal.
 16. The systemaccording to claim 1, further comprising: a light source outputtinglight energy at a wavelength in the range of about 2.05 μm to about 2.30μm, said light source illuminating the area of interest.
 17. The systemaccording to claim 16 wherein said light source is selected from thegroup consisting of a laser, halogen light, infrared light, andlight-emitting diode.
 18. A method for detecting ice within an area ofinterest, said method comprising: measuring a first radiance of the areaof interest at a first spectral band in the range of about 2.05 μm toabout 2.15 μm; measuring a second radiance of the area of interest at asecond spectral band in the range of about 2.15 μm to about 2.30 μm;calculating a radiance ratio of said first radiance and said secondradiance; and determining whether said radiance ratio is within apredetermined critical radiance ratio range, if said radiance ratio iswithin said predetermined critical radiance ratio range then determiningif a specular reflection is present by determining if said firstradiance is greater than a predetermined critical radiance andoutputting an ice-present warning.
 19. A method for detectingsupercooled liquid water droplets within an area of interest, saidmethod comprising: measuring a first radiance of the area of interest ata first spectral band in the range of about 2.05 μm to about 2.15 μm;measuring a second radiance of the area of interest at a second spectralband in the range of about 2.15 μm to about 2.30 μm; calculating aradiance ratio of said first radiance and said second radiance; anddetermining whether said radiance ratio is within a predeterminedcritical radiance ratio range, if said radiance ratio is within saidpredetermined critical radiance ratio range then measuring a temperatureof the area of interest and determining if said temperature is within apredetermined critical temperature range and outputting asupercooled-liquid-water-droplets-present warning.
 20. A method fordetecting supercooled large droplets (SLD) within an area of interest,said method comprising: measuring a first radiance of the area ofinterest at a first spectral band in the range of about 2.05 μm to about2.15 μm; measuring a second radiance of the area of interest at a secondspectral band in the range of about 2.15 μm to about 2.30 μm;calculating a radiance ratio of said first radiance and said secondradiance; and determining whether said radiance ratio is greater than apredetermined critical radiance ratio, if said radiance ratio is withinsaid predetermined critical radiance ratio then calculating a dropleteffective radius and determining if said droplet effective radius isgreater than a predetermined critical droplet radius and outputting asupercooled-large-droplets-present warning.